Reef shallows sea snake description

Also known as Dubois’ sea snake, the reef shallows sea snake (Aipysurus duboisii) is named after Charles Fréderic Dubois, a Belgian naturalist in the 1800s (4). The head of the reef shallows sea snake is usually as wide as, or slightly wider than, its body (3), and its nostrils are positioned higher up on its head than in terrestrial snakes, which makes it easier to breathe when it surfaces (3)(5). The reef shallows sea snake has a long and moderately enlarged tail (3) and, as in other sea snake species, the end of its tail is flattened and paddle-like, enabling this marine reptile to swim efficiently (5).

In terms of colour and pattern, the reef shallows sea snake is extremely variable (2)(3)(6)(7). Interestingly, there appears to be a geographical split in terms of colouration, with darker specimens usually being found west of the Torres Strait, and paler individuals to the east (7).

The upper side of the reef shallows sea snake ranges from whitish-beige or salmon to brown or purplish-brown, and is patterned with dark or cream bands or yellowish blotches (2)(3)(6). These markings are usually the result of wedge-shaped areas extending upwards from the underside (7), which varies from creamy white to dark brown (3)(6). The chin and throat regions are generally paler than the rest of the body (3).

Most of the scales on the head of the reef shallows sea snake are small and fragmented (2)(3)(7)(8)(9), while the scales on the underside of the body are almost three times as wide as those on the dorsal surface (3). Each of the dorsal scales has a fine, pale line running along its edge (2)(3), which can sometimes give the reef shallows sea snake a reticulated appearance when the body is extended (6)(7). The dorsal scales are generally smooth, while those on the underside are usually weakly keeled(2)(3).

The reef shallows sea snake’s skin is sometimes encrusted with a variety of marine life, from seaweed to polychaete worms, particularly on the top of the head (1)(3). Although the reef shallows sea snake is usually relatively small, only reaching lengths of between 80 and 110 centimetres (2)(3), one recorded individual attained an impressive length of 140 centimetres (1).

Related species

Reef shallows sea snake biology

Like all species within the Aipysurusgenus, the reef shallows sea snake is an entirely aquatic species, never venturing onto land, not even to breed (11). This species is active during the day, although it spends much of its time resting under sea fans or hidden within seaweed (3).

Despite being an air-breathing animal, the reef shallows sea snake is capable of remaining underwater for up to two hours at a time, before surfacing to breathe again. Its single, elongated lung, which extends for almost the entire length of its body, is highly efficient for gas exchange, and sea snakes are also able to absorb oxygen through their skin when underwater. All sea snakes have specialised nostril valves which prevent water from entering the lung when submerged (7).

Living in a marine environment poses several challenges. As in other sea snake species, the reef shallows sea snake has a specialised gland under its tongue which enables it to excrete excess salt from its body. Additionally, other marine species such as algae and barnacles often become attached to the reef shallows sea snake’s skin, a problem which is solved each time the snake sheds its skin, which usually happens every two to six weeks (7).

Although the reef shallows sea snake’s venom is highly toxic (2)(3), this species is not thought to pose much of a threat to humans, as it is a relatively small snake and does not yield much venom (3).

Like most species of sea snake, the reef shallows sea snake is viviparous, meaning that it gives birth to live young rather than laying eggs (3)(7). Mating in sea snakes is a lengthy affair, and the males are unable to disengage from the female until copulation is complete. In northern Australia, the gestation period of the reef shallows sea snake is between six and seven months, with births occurring between March and June (7). Reef shallows sea snake litters are relatively small (6), consisting of about four or five young on average (7), and the young are relatively large (6)(7). Female reef shallows sea snakes are thought to reproduce every year (7).

The reef shallows sea snake has a more varied diet than some other sea snakes (9), opportunistically feeding on a wide range of reef fish species (1)(3)(6)(7)(9). For example, it is known to take blennies (Blennidae species), parrotfish (Scaridae species) and surgeonfish (Acanthuridae species) (7), as well as moray eels (Muraenidae species) (3)(7). The reef shallows sea snake stalks its prey along the sea bed (3), and is thought to feed in the early evening (7). The seaweed which sometimes grows over its skin is useful as camouflage, helping the snake to ambush its unsuspecting prey (3).

Reef shallows sea snake range

The reef shallows sea snake is a widespread species, but it is patchily distributed (1). This species occurs throughout northern tropical Australia from Western Australia to the southern Great Barrier Reef, and its range extends east to Papua New Guinea and New Caledonia (1)(2)(7)(10), as well as the Loyalty Islands and Indonesia (10).

Species with a similar range

Reef shallows sea snake habitat

As its name suggests, the reef shallows sea snake is primarily found in shallow-water habitats adjacent to coral reefs (1)(7), such as over sponges, sand, sea grass beds or among broken corals (1)(3)(9). Although often in water just 3 to 4 metres deep (7), this species can be found at a range of depths (1)(2)(9), usually down to about 50 metres (1)(2)(3)(6). Unusually, a shrimp trawl once caught a reef shallows sea snake at a depth of 80 metres (1)(3).

Interestingly, out of the 14 sea snake species found on the Great Barrier Reef, the reef shallows sea snake is just one of 2 species that are restricted to reefs (9), yet in New Caledonia this species is reported to never frequent coral reef areas (3).

Reef shallows sea snake status

Reef shallows sea snake threats

There have been declines in the number of reef shallows sea snakes on Ashmore Reef in Western Australia, as well as other reported regional declines, but the reasons for these are unknown. Trawl fisheries have reported reductions in sea snake bycatch over the last few decades, but it is unknown whether such reductions are due to changes in fishery patterns or to declines in abundance of the species. However, trawling activities in the vicinity of reefs is believed to be a potential threat to the reef shallows sea snake (1).

It is thought that the reef shallows sea snake may be impacted by the degradation of its coral reef habitat, either through direct destruction from expanding oil and gas development, or as a result of the effects of climate change, such as increased sea surface temperatures and coral bleaching. Such impacts may lead to a decrease in prey abundance, and the loss of refuge sites for the reef shallows sea snake (1).

Reef shallows sea snake conservation

The reef shallows sea snake is not currently considered to be at risk of extinction, and no targeted conservation measures are known to be in place for this species at present. However, it is offered some protection as a result of its occurrence in a number of Marine Protected Areas (1), including the Great Barrier Reef Marine Park, and Ashmore Reef in Western Australia, which is a Commonwealth Reserve (7). Additionally, recommendations have been made to monitor bycatch of the reef shallows sea snake, and to encourage the use of exclusion devices in fisheries, to reduce the level of bycatch(1).

All sea snake species in Australia are protected under their classification by the Department of Environment and Water Resources as ‘Listed Marine Species’. In addition, sea snakes are protected under the Environment Protection and Biodiversity Conservation Act 1999, while the Australian Fisheries Management Act 1991 requires fisheries to avoid impacting on protected or threatened species, including sea snakes. A three-year study has been instigated to develop and implement a long-term bycatch monitoring programme for Australia’s Northern Prawn Fishery, which has the largest impact of any Commonwealth-managed fishery on protected sea snake populations (1).

Since 2003, industry workshops have been jointly run by Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO) and Australia’s Fisheries Management Authority (AFMA) to train prawn fishery crew members on how to identify, photograph and record information regarding sea snake capture during the main prawn seasons (1).

Authentication

Glossary

Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.

Bycatch

In the fishing industry, the part of the catch made up of non-target species.

Dorsal

Relating to the back or top side of an animal.

Genus

A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Gestation

The state of being pregnant; the period from conception to birth.

Gland

An organ that makes and secretes substances used by the body.

Keel

A projecting ridge along a flat or curved surface, particularly down the middle.

Polychaete worms

Polychaeta means ‘many bristled’; this class of worms are segmented and bear many ‘chaetae’ (bristles).

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